Give Every Item a Home
The single most powerful organizing principle: every object you own should have a specific, intentional place it belongs. When something doesn't have a home, it becomes clutter by default. Start with one drawer or shelf, assign a spot for each item and commit to returning it there. That one habit creates a cascade of calm throughout your space.
Label the space, not just the bin. A label on the shelf itself means the item returns to the right place even when the bin is out.